There is known an image generating system which can generate an image as viewed within a virtual three-dimensional or object space from a given viewpoint. Such a system is very popular since one can experience a so-called virtual reality through it. Now considering a image generating system for playing a gun game, a player (or operator) can enjoy a three-dimensional shooting game by manipulating a gun-shaped controller (or shooting device) to shot targets such as enemy characters (or model objects) and the like which are displayed on a screen.
In order to improve the virtual reality for a player in such an image generating system, it was an important technical problem to produce more realistic images. It is thus desired that when, for example, a glass plate is broken by impact such as a bullet, the broken glass may more realistically be represented.
In the conventional image generating systems, however, when a bullet has hit a glass plate, the image is simply replaced by an image representing the broken glass plate which was previously provided. Independent of the hit position or the power of a bullet, the same image of a broken glass plate is shown. The representation is monotonic and lacks in reality.
According to such a technique, once a glass plate was broken by a first bullet, the image will not change even if the glass plate is hit by the succeeding bullets. Consequently, the representation was insufficient when it is possible that the glass plate is hit by many bullets in high-speed continuous shooting.